Light valve



Jan. 3, 1939. 3 F, MlLLER 2,142,573

LIGHTVALVE Filed June 24, 1935 2 Sheets-Sheet l I NV EN TOR.

ATTORN Y Jan. 3, 1939. F, 2,142,573

LIGHT VALVE Filed June 24, 1935 2 Sheets$heet 2 m *5 a PIE. 8.

INVENTOR. 5uQTo/v F M/LLEQ Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE.

LIGHT VALVE Application June 24, 1935, Serial No. 28,109

SCIaims.

This invention relates to light valves for photographically recording sound upon a moving light sensitive film.

One object of the invention is to provide a light valve construction which will permit the recording on a moving film of a graphic representation of sound waves in such a manner as to have the graphic representation of as large an amplitude as possible with a relatively small movement of the speech current carrying conductor.

This is accomplished by providing the light valve with an aperture through which a beam of light is protected upon a uniformly moving light sensitive film. The aperture is in the form of an isosceles triangle having a very small height in comparison to its base. A speech current carrying conductor is placed over the triangular aperm ture parallel to its base so as to cover part of the aperture when no current is fiowing. When a modulated alternating current is passed through the conductor the interaction between the magnetic force set up by the modulated current and a strong magnetic field provided adjacent the aperture causes the conductor to vibrate in accordance with the amplitude and frequency of the sound being recorded. This vibration allows a greater or less length of the aperture to be exposed to the beam of light.

Another object of the invention is to keep the zero line or center of modulation of the wave forms always in the center of the sound track.

Another object of the invention is to reduce the ground noise due to the grain of the emulsion, or to dirt, oil, etc., adhering to the clear portions of the sound track (positive film).

Heretofore, sound recording devices of the variable area type obtained ground noise reduction either by biasing the current carrying vibratory.

conductor or by the use of auxiliary shutters which were automatically controlled to follow the envelope of the wave forms and thus allow only the areas between the successive wave forms to be exposed. Both of these methods have inherent disadvantages: the use of shutters entails rather complicated and sensitive apparatus which, due to electrical or mechanical lag or to faulty adjustment, may cause clipping of the sound peaks; especially is this true in the case of stacatto type sounds where the rise in amplitude is practically instantaneous; when biasing of the conductor is employed, the zero or center of modulation is moved as close as possible to the edge of the clear portion of the sound track; that is, all the peaks of both the high and low level sounds are as close as possible to one edge of the track; due to the shrinkage of the film or inaccuracies in the reproducing machine, the film has a tendency to weave sideways wr; en passing the point of sound translation; this weave is at times sufiicient to allow 5 one end of the light slit to cut off some of the wave peaks; although the peaks of the high level sounds may be cut off a substantial amount without any apparent distortion of the reproduced sound, this is not true of the low level peaks. 1

By keeping the center of modulation always in the center of the sound track, there will be no chance of clipping the ow level peaks.

Referring more particularly to the drawings,

Fig. 1 is an enlarged fragmentary view of the 15 triangular aperture and its accompanying speech current carrying conductor.

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 3'showing my improved form of light valve for recording variable area.

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2.

Fig. 4 is a schematic view showing the application of noise reduction to my improved form of light valve. 25

Fig. 5 is an enlarged fragmentary view of the section of sound film showing a double edged variable area sound track as recorded by my improved light valve.

Fig. 6 is an enlarged fragmentary view of a section of sound track on a negative film.

Fig. 7 is an enlarged fragmentary view of a section of sound track on a positive film.

Fig. 8 is a diagrammatic view showing the method of regulating the noise reduction.

Referring now to Figs. 2 and 3, the light valve l comprises an upper magnetic frame 2 having a pair of depending legs 3 and 4. A lower base plate 5 is secured to the legs 3 and 4 such as by screws 6. The frame 2 has a hollow core 7 comprising one of the pole pieces and is provided with a magnetizing coil 8. Direct current of as constant a value as possible is passed through the coil 8 to produce the high magnetic flux between the core I and a pole piece 9 secured to the base plate 5 in substantial alignment with the core 1. The pole piece 9 and also the base plate 5 are provided with an aperture Ill to allow a beam of light to be pro jected therethrough. The triangular aperture Ii comprising the light slit is formed by means of three plates l2, l3, and H, (Figs. 1 and 2) which are secured to the upper surface of the pole piece 9 by means of a pair of clamping pieces l5 and I 6. Clamping screws ll serve to clamp the pieces l5 and IS in position. The aperture H is of very small height in comparison to its base, being in this instance about 1 mils high and about mils long. A pair of bridges l8 and I9 is provided, one on either side of the pole piece 9 parallel to the base o the aperture H These bridges l8 and I9 are preferably composed of an insulating material such as Bakelite or hard rubber and are secured to the base plate 5 as by screws 28 and 2|. The forward edges of the bridges l8 and 19 have plates 22 and 23 secured thereto as by screws 24 and 25. These plates 22 and 23 project above the surface of the bridges l8 and I9 and serve as supports on which a vibratory conductor 21 is placed. Clamping pieces 28 and 29 are secured to the plates 22 and 23 as by screws 38 and 3| (Fig. 2). Each of the bridges l8 and I9 is provided with a pair of adjusting jaws 32 and 33. These jaws are preferably of a spring material and are secured to the rear ends of the bridges as by screws 34 and 35. The forward ends of the jaws 32 and 33 are engaged by adjusting screws 36 and 31. Adjustment of the conductor 21 is accomplished by rotating either of the adjusting screws 36 and 31. When the proper adjustment has been effected, the conductor 21 is clamped in position by means of the clamping pieces 28 and 29. The ends of the conductor 21 are secured to windlasses 38 and 39 which are rotatably secured within insulated blocks 48 and 4!. Before reaching the Windlass 39, the right hand end of the conductor is looped over a spring pressed arm 6| which is pivotally mounted to the base as at 62. The arm 6! allows for easier adjustment of the tension of the ribbon and prevents undue tension from being applied. The blocks 48 and 4| are secured to the base plate 5 by means of screws 42. Each of the windlasses 38 and 39 is electrically connected to terminals 43 and 44 (insulated from the base plate 5) which in turn are adapted to be connected to a suitable sound amplifying system.

Referring to Fig. 4, I will now describe the application of noise reduction to the above mentioned type of valve. The sounds to be recorded upon a light sensitive film 45 are received in a microphone 46 and amplified by a suitable amplifier 41. The speech currents thus amplified are passed through a transformer 48 and thence by means of conductors 49 and 58 are passed through the vibrating conductor 21. Interaction between the magnetic force set up by the modulated alternating current passing through the conductor 21 and the strong magnetic field set up between the pole pieces 1 and 9 cause the conductor 21 to vibrate in accordance with the amplitude and frequency of the sound waves and thus vary the length of the triangular aperture ll exposed to a beam of light from an exciter lamp 52. Light from the exciter lamp 52 is collected by means of a condenser lens 53 and is focused at a point adjacent the slit H from whence it is projected onto the moving film 45 by means of an objective lens 54. Noise reduction is obtained by'holding the center of modulation of the conductor 21 in a position as shown by the dot and dash lines 55 (Fig. 1) when no or little sound is being recorded. This is accomplished by passing a biasing current from a battery 6| (Fig. 4) through the conductor 21. An amplifier 5B and rectifier 51 are shunted across the conductors 49 and 58. In recording low level sounds, a very small amount of current is passed through the amplifier and rectifier combination 56 and 51 but when high level sounds are recorded, a correspondingly greater amount of ourrent is passed through the amplifier 56 and rectifler 51. The resulting rectified current is passed through the conductor 21 in a direction opposing the steady biasing current from the battery 6| thus neutralizing the biasing effect. Thus the center of modulations for high level sounds is moved'to a position shown by the full lines 21 (Fig. l).

The biasing of the conductor 21 may also be obtained by applying the rectified current from the rectifier 51, which varies in accordance with the amplitude of the sounds being recorded, directly to the conductor 21. In this case, the normal position of the conductor at low level recording would be mechanically adjusted so that it would cover a greater part of. the slit II as indicated by the dot and dash lines 55 (Fig. 1). With the increase in amplitude of sound recorded, the corresponding increase of the rectified current from the rectifier 51 would shift the center of modulation of the conductor 21 to the position shown by the full lines (Fig. l).

The amount of biasing of the conductor is generally dependent upon the kind of sound being recorded. When recording dialogue or music in which the volume is low or where the change in volume is gradual the mean biasing position of the conductor may be brought nearer the apex of the triangular aperture than in the case of recording staccato sounds such as are produced by a harp or piano. In recording the latter type of sound, more lee-way has to be given to the conductor to prevent the higher level wave forms from being clipped before the conductor has a chance to be moved toward its unbiased position. This change in biasing position of the conductor is accomplished by means of potentiometers 58 and 59 (Fig. 4) and may be effected during the recording wherever the tempo of the sound is changed. The amount of biasing is generally measured by the amount of margin between the opposite depressions of a wave form, for example, D1 and D2 (Fig. '7). Referring to Fig. 8, the margin may also be determined by the distance from the apex of the triangular aperture to the position of conductor 21 at the upper limit of its excursions as shown by the dotted lines 68. In setting the biasing position of the conductor 21, the potentiometer 58 or 59 is manipulated until the distance X, representing one-half the amplitude of the conductor excursions, is allowed to reach a certain percentage of the distance D; this, of course, depending on the type of sound being recorded. In recording soft sounds, the distance X may be allowed to cover as much as 75% of the distance D.

In the example shown in Fig. 8, the potentiometer 58 or 59 is set so X will equal one-half D when the conductor is in its biasing position. Thus the margin for low level sounds is indicated by the dimension M. When X exceeds one-half of D the change in biasing current causes the mean position of the conductor to be moved downward so as to maintain the same ratio of X to D. This ratio is kept constant until the conductor 21 reaches the unbiased position as shown by the dotted lines 21' at which point the mean position of the conductor. 21 will lie half way between the apex and. the base of the triangle. Here the margin M will be seen to be considerably larger allowing for an increase in ground noise. This is, however, negligible due to the fact that the sound level is higher in proportion. As higher amplitudes are recorded, the

center of modulation of the conductor 21 re- 15 mains the same while the margin again becomes smaller as at Mh.

Referring to Fig. 5, the center of modulation for each edge of the positive sound track is indicated by the center lines BI and 62. Where no sound is recorded on the film, only a narrow path of transparency 63 traverses the center of the soundtrack. As modulations are recorded and increased, the centers of modulation GI and 62 are spread apart until they reach their unbiased position.

Due to the fact that the edges of the sound track are formed by the acute angle between the conductor 21 and the triangular aperture I l these edges will not form sharp lines but will gradually pass from clear transparency to opacity as shown in Figs. 6 and 7. In the negative film 65 (Fig. 6) the sound track starts with a faint outline at 66 and gradually darkens until it is pure black at the core. When the negative is printed onto the positive print 61, the latter is given a rather hard development, that is, the positive is made extremely sensitive to the shading of the negative so that except for a small zone 68, the clear portion 69 will be entirely transparent. The amount of distortion produced by the shaded zone 68 is negligible due to the fact that its dimension as measured transverse of the direction of film travel remains constant and thus is unable in itself to effect a. varying change in light passing therethrough; it being understood, of course, that the reproduction of sound is dependent upon a change in the amount of light emanating from a slit placed transverse of the film travel.

Having thus described the invention what is claimed as new and desired to secure by Letters Patent is:

1. A light translating device comprising a magnetic frame, a pair of poles on said frame, a triangular light aperture having straight edges and of uneven width, and a flexible current carrying ribbon conductor disposed across said aperture parallel to its longest dimension and adapted to be vibrated in accordance with the current flowing through said conductor, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

2. A light translating device comprising a magnetic frame, a pair of poles on said frame, a straight sided triangular light aperture, a flexible current carrying ribbon conductor disposed across said aperture parallel to the base of said aperture and adapted to be vibrated in accordance with the current flowing through said conductor, and independent adjusting means on either side of said aperture for adjusting the position of said conductor, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

3. In a light valve the combination of a magnetic frame, a pair of hollow pole pieces on said frame in substantial alignment with each other, a straight sided triangular light aperture, and a vibratory current carrying ribbon conductor disposed across said aperture parallel to its base and adapted to be vibrated in accordance with the wave form of the current passed through said conductor, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

4. In a light valve, a magnetic frame, a pair of hollow pole pieces on said frame, a light aperture, said aperture being in the form of an isosceles triangle having a much shorter height than base length, and a vibratory current carrying ribbon conductor disposed across said aperture parallel to its base and adapted to vibrate in accordance with the amplitude of an alternating current passed therethrough so as to expose a varying length of said aperture, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

5. In a light translating device, the combination of a magnetic frame, a hollow pole piece on said frame, a magnetic plate secured to said frame, a second hollow pole piece on said plate, an aperture in substantial axial alignment with said pole pieces and in the form of an isosceles triangle having a much shorter height than base length, and a vibratory current carrying ribbon conductor disposed between said first pole piece and said aperture parallel to its base and adapted to vibrate perpendicular to said base in accordance with an alternating current passed therethrough so as to expose a varying length of said aperture which varies in accordance with the amplitude of the current, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

6. In a light translating device, the combination of a magnetic frame, a hollow pole piece on said frame, a magnetic plate secured to said frame, a hollow pole piece on said plate in substantial alignment with said first mentioned pole piece, a plurality of aperture forming members lying in a single plane and secured to said second mentioned pole piece to form an isosceles triangle in substantial axial alignment with said pole pieces and having a much shorter height than base length, and a vibratory current carrying ribbon conductor lying in a second plane parallel to said first plane and disposed across said aperture parallel to its base and adapted to vibrate in said second plane in accordance with an alternating current passed therethrough so as to expose a varying length of said aperture which varies in accordance with the amplitude of the current, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

7. In a light translating device, the combination of a magnetic frame, a hollow pole piece on said frame, a magnetic plate secured to said frame, a hollow pole piece on said plate in substantial alignment with said first mentioned pole piece, a plurality of aperture forming members secured to said second mentioned pole piece to form an isosceles triangle in substantial axial alignment with said pole pieces and having a much shorter height than base length and lying in a single plane, a vibratory current carrying ribbon conductor disposed across said aperture parallel to its base and adapted to vibrate in accordance with an alternating current passed therethrough so as to expose a varying length of said aperture which varies in accordance with the amplitude of the current, and independent adjusting means on either side of-said aperture for adjusting the position of the said conductor, an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

8. In a light translating device, the combination of a magnetic frame, a hollow pole piece on said frame, a magnetic plate secured to said frame, a hollow pole piece on said plate in substantial alignment with said first mentioned pole piece, a plurality of aperture forming members secured to said second mentioned pole piece to form an isosceles triangle in substantial axial 7 current, means for adjusting said conductor relative to said aperture, and clamping means'on either side of said aperture for securing said conductor in place after said conductor is adjusted. an edge of said conductor and certain edges of said aperture being adapted to define an image to be projected.

' BURTON F. liflILER. 

